Avalanche Forecast

Issued: Feb 12th, 2018 4:57PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs and Persistent Slabs.

jmcbride, Avalanche Canada

South Columbia.

New snow and wind on Tuesday will add to an already complex and tricky snowpack. Choose conservative terrain and minimize your exposure to overhead hazard. Large avalanches may run long distances.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

TUESDAY: Snow. Accumulation 10-15 cm. Ridge wind moderate to strong, southwest. Temperature -5. Freezing level 800 m.WEDNESDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, west. Temperature -8. Freezing level 500 m.THURSDAY: Mix of sun and cloud. Ridge wind light, southwest. Temperature -10. Freezing level valley bottom.

Avalanche Summary

On Sunday a few small natural (size 1-1.5) storm slab releases were observed on northerly aspects above 2000 m.A very large, widespread avalanche cycle was observed on Thursday, with a few events continuing on Friday. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was smashed. These failed on all of the persistent weak layers discussed in the snowpack section. Avalanches involving only the recent storm snow were also very large. Explosives continued to produce large persistent slabs on Saturday, and a few wind-triggered slabs were also reported. The natural cycle seems to have diminished however, human-triggering remains a real concern.

Snowpack Summary

Winds have shifted 30-40 cm recent storm snow into wind slabs on lee slopes. Alpine and open treeline areas have seen variable wind-affect while a sun crust exists on solar aspects, and a rain crust is present below 1600 m.Below the snow surface several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or the other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Problems

Wind Slabs

New snow and wind will add to recently formed wind slabs and cornices on lee slopes. On solar aspects and at lower elevations the new snow will overlie an old crust. Pay attention to the bond between the old and the new snow.

Give cornices a wide berth when travelling on or below ridges.Travel on ridgetops to avoid wind slabs on slopes below.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1.5 - 3

Persistent Slabs

Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Avoid steep convexities or areas with a thin or variable snowpack.Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 13th, 2018 2:00PM